Total Knee Replacement

Total Knee Replacement

By Dr. KM Liau

Total knee replacement offers the greatest quality of life improvement of all operations. It has one of the highest success rates and one of the best outcomes.

KNEE REPLACEMENT COMPONENT

There are 3 separate components of TKR:

1. Femoral component

2. Polyethelene insert

3. Tibial component

FEMORAL COMPONENT

The upper part of the replacement knee joint consists of a contoured metal shield that fits around the lower end of the femur.

The inner surface can be fixed to the cut bone surfaces by the surgeon's choice of bone ingrowth or bone cement.

The outer surface of the contoured metal shield is shaped to allow the knee cap (patella) to slide up and down in its groove.

The surgeon may choose to retain the natural knee cap or re-surface it. In this case a polyethylene button will be cemented in place.

POLYETHELENE INSERT

This is the middle component.

It is clipped into the tibial tray to serve as the new knee bearing surface.

TIBIAL COMPONENT

The lower part of the replacement knee joint is comprised of a flat metal plate and stem that your surgeon will implant in the tibial bone, as shown in the movie above.

The tibial tray can be either cobalt chrome alloy or titanium alloy.

It can be fixed by either cement or bone "ingrowth".

Implant Design - Unconstrained System

Unconstrained designs are characterized by very low constraint over the entire range of normal displacements.

Features:

1.Allow for minimal bone resection; in the event of failure, may be converted to semi-constrained implant.

2.Stability is dependent on the collateral ligaments

3.All normal movements can occur at the joint, thus reducing the incidence of mechanical loosening.

4.Precise surgical technique is required.

5.Long term results greater than 10 years are excellent.

Implant Design - Semi-Constrained System

Semiconstrained designs have near-physiologic constraint that increases over the range of normal displacements.

Loose link between the femoral and tibial components allow for inherent stability.

For such knees to be effective the major knee ligaments (cruciates and collaterals), or at least most of them, had to be intact.

Stability after knee replacement was provided by the patient's own ligaments, rather than the replacement itself.

Implant Design - Constrained Knee System

For unstable knees (Valgus / Varus Instability)

Constrained designs are characterized by constraint that exceeds physiologic levels and increases sharply over the range of displacements.

Legacy Constrained Condylar Knee (LCCK)

For unstable knees (Valgus / Varus Instability)

For patients who lack functional collateral ligaments or whose knees cannot be stabilized by the usual soft tissue releases, the Constrained Condylar Knee (CCK) system features an elevated tibial spine and deeper femoral intercondylar box.

A close fit between the spine and box provides stability as the mechanical roll back is induced, inhibiting posterior subluxation, limiting varus/valgus movement and internal/external rotation.

This design accommodates a theoretical range of motion in excess of 120 degrees.

Implant Design - Hinged Knee

Ease of insertion and rapid post-op rehabilitation .

The rate of mechanical loosening is extremely high. It allows flexion and extension only, thus the torsional stresses will cause high wear rate.

Only used for difficult revision cases in the elderly (eg. severely incapacitated rheumatoid arthritic patient) and low demand patients.

Implant Design Link List

Implant Design

Total Knee Replacement implant design

Total Knee Replacement

Total Knee Replacement

Goals of Surgery

1. Relief of pain

2. Correction of knee joint deformity

3. Restoration of knee joint motion

4. Restoration of knee joint function

creation of a stable knee joint.

Mechanical Axis

The mechanical axis of the knee is a line extending from the center of the hip joint to the middle of the ankle joint. This line is practically perpendicular to the ground.

In a healthy, well aligned knee joint, the mechanical axis passes through the middle of the knee.

The surgeon must restore the mechanical axis of the knee joint during the total replacement surgery, i.e. he must put the new knee joint in such a position that the mechanical axis passes again through the middle of the new knee joint.

The surgeon call it " realigning of the total knee joint".

In this "realigned" position, the patella glides symmetrically in its groove.

A total knee prosthesis put in badly aligned knee joint will be overloaded, the patella (or its prosthesis) will dislocate and eventually the whole total knee joint will loosen or break down.

Disturbance of Knee Joint Mechanic

The mechanical axis of the limb is distorted and does not pass through the middle of the knee joint.

The ligaments are usually shrunken to keep the knee joint in the persistent wrong position.

There are also contractures in the joint capsule keeping the knee joint in persistent bent position of the knee joint (Contracture).

The surgeon must correct the distorted position of the knee joint and restore the balance of the soft tissues.

All this can be achieve by making precise cuts through the bone ends so that when the prosthesis is put in place the mechanical axis of the knee joint will be restored, the ligaments will be tight, and the contractures will be corrected.

Making Precise Cuts

All damaged knee joint surfaces will be removed with saws by using specialised jigs.

The purpose is to provide close fit for the insertion of the components of a total knee prosthesis.

Trial Prosthesis To Assess The Precision Of The Cuts

A rectangular metal block (gray) is put in between the cut joint surfaces to check the alignment.

The block is equally thick as the future total knee prosthesis.

With this block in place the surgeon will assess whether the cuts are appropriate to restore the mechanical axis of the knee joint.

If this assessment showed the right alignment of the mechanical axis of the new total knee, the surgeon then goes on to assess the function of the total knee prosthesis.

For this purpose, the surgeon places the trial knee joint prosthesis (gray) on the prepared bone ends and examines the range of motion and stability of the new knee joint.

Definitive Total Knee Prosthesis

If the range of motion is good, the stability of the joint is restored (the ligaments have proper tension) and the mechanical axis is restored, the definite prosthesis components are placed into position definitively.

The femoral component of a knee prosthesis is a shell like plate, made from alloy.

The tibial component is a plate made of polyethylene (green), with small excavations for the engaging articular surface of the femoral component.

Very often, the polyethylene plate is enclosed in a metallic envelope - metal backing - (blue) , especially in cementless knee prostheses.

The surgeon pushes these components in place on the prepared bone surfaces and controls again the motion, stability and mechanical axis of the new knee joint.

PATIENT SELECTION

1. Preop knee flexion more than 90 degree and the patient should be capable of reaching 120 degree of flexion.

2. The patient should have stable and functional collateral ligaments.

3. If the patient has an angular deformity, it should be less than 20 degree because it is more difficult to achieve ligament balance in these patients.

PRE-OP CONDITIONING

To help prepare the patient for surgery, it is helpful for the patient to perform mobility exercises to prepare the ligaments and muscles for the postoperative rehabilitation protocol.

SURGICAL PRINCIPLES

1. Balance the flexion and extension gap.

2. Clear the posterior osteophytes.

3. Release the posterior capsule.

4. Reproduce the joint line.

The critical goal is to create a rectangular and symmetrical flexion gap between the femur and tibia.

IMPORTANCE OF REPRODUCING JOINT LINE

Alteration of the joint line can cause patellofemoral issues and limit the degree of flexion.

An elevated joint can cause tibiofemoral tightness in roll-back and thus restrict flexion.

The alteration of the joint line can be minimized by accurately measuring for the femoral component size and performing a posterior capsulotomy to correct flexion contractures.

CASE STUDY

60 year old lady presented with chronic bilateral knee pain for past 3 years. The pain has become unbearable and disturbs her daily activity.

Note the bilateral genu varum.

Intercondylar distance measures 10 cm

LATERAL VIEW

No genu recurvatum or fixed flexion deformity noted

PLAIN X-RAY

Decreased joint space over medial and lateral compartment

Osteophyte formation

Subchondral sclerosis

Subchondral cyst

X-RAY LATERAL VIEW

Decreased Patello-Femoral joint space with osteophyte formation.

OPERATION

Silicone pad for placement of foot to keep the knee in 90 degree flexion during operation

CLEAN & DRAPE

Povidone iodine is used for sterilizing the surgical field.

Povidone is the short form of polyvinylpyrolidone, the large molecular weight carrier of iodine.

Iodine once exposed to air will be oxidized to iodide.

Iodide will break the disulfide bond of protein of bacterial cell wall thus killing it.

INCISION AND EXPOSURE

Medial parapatellar approach is recommended.

With the patient in the supine position and the knee slightly flexed, make a straight midline incision with a gentle medial curve around the medial border of patella.

Begin the incision medial to the quadriceps tendon and 3cm-5cm above the superior pole of the patella.

Extend it distally to below the level of the tibial tubercle

CAPSULAR INCISION

The capsule is incised over medial side for the following reasons:

1. Easier access to diseased medial compartment.

2. Prevent fibrosis over lateral side of patella that will predispose to patella dislocation post-op.

SYNOVIAL FLUID SAMPLING

Sample of synovial fluid is send for microbiological culture and sensitivity before proceeding into the joint.

PATELLA RETRACTION

Patella is retracted laterally.

Do not evert the patella as it will cause risk of patella tendon rupture.

Note the cartilage erosion over femoral condyle with exposed subchondral bone.

DEGENERATED FEMORAL CONDYLE

Note the degenerated cartilage, exposing the subchondral bone.

FAT PAD EXCISION

Retropatellar fat pad is excised to prevent post-op arthrofibrosis.

VARUS RELEASE

With the knee extended, elevate a subperiosteal sleeve of soft tissue from the proximal medial tibia, including the deep medial collateral ligament, superficial medial collateral ligament, and insertion of the pes anserinus tendons.

Continue the elevation with a periosteal elevator to free the posterior fibers.

To improve exposure during the release, retract this subperiosteal sleeve using a Homan retractor.

Release the insertion of the semimembranosus muscle from the posteromedial tibia.

Continue the release distally on the anteromedial surface of the tibia for 8cm-10cm and strip the periosteum medially from the tibia.

For more severe deformities, continue subperiosteal stripping posteriorly and distally.

If flexion contracture is present, release or transversely divide the posterior capsule.

WHITESIDE LINE & TRANS-EPICONDYLAR LINE

Whiteside line is the vertical line cutting through the middle of distal femoral sulcus.

Trans-epicondylar line is the horizontal line linking the medial and lateral epicondyle.

DRILL BIT

9.5mm diameter drill bit is used to initiate the starter hole.

DISTAL FEMUR PREPARATION

The starter hole is created at the intersection between the vertical Whiteside Line and the horizontal Epicondylar Line.

The hole is placed medial and anterior to the anteromedial corner of the intercondylar notch.

Initiate an opening in the femoral canal with the 9.5mm diameter drill bit.

DISTAL FEMORAL RESECTION GUIDE

IM alignment rod is removed prior to resecting the distal femur.

Distal femur is resected with either the
standard resection slot, which provides a 9mm resection from the prominent distal condyle, or the +4mm resection slot which provides a 13mm resection.

If headless pins are used, the resection block can
be adjusted 2mm proximally or distally.

ASSEMBLE DISTAL RESECTION GUIDE

Assemble the Distal Resection Guide and Valgus Alignment Guide onto the intramedullary alignment rod.

FEMORAL VALGUS RESECTION GUIDE

Valgus resection guide is set to 5 to 7 degree of valgus.

MECHANICAL AXIS

The 5 to 7 degree valgus cut is made in order to get a distal cut that is perpendicular to the mechanical axis.

DISTAL FEMORAL RESECTION

Ensure that the resection block is seated flush against the anterior rough cut and lock the
assembly with the thumbscrew.

Fix the distal femoral resection block to the anterior cortex with two headless pins.

DISTAL FEMORAL RESECTION USING STANDARD SLOT

Resect the distal femur using the standard resection slot which provides a 9mm resection from the prominent distal condyle.

DISTAL FEMORAL CUT COMPLETED

The final distal femoral resection is shown here.

EXTRAMEDULLARY TIBIAL GUIDE

Components: (from top to bottom)

1. Cross head with pin

2. Resection guide

3. Ankle yoke

EXTRAMEDULLARY TIBIAL GUIDE

Use the adjustment screw at the ankle to align the
resection guide.

The long axis of the tibial resection guide should be
parallel to the tibia.

EXTRAMEDULLARY TIBIAL GUIDE

Position the anterior pin of the resection crosshead over the footprint of anterior cruciate ligament.(ARROW)

CROSSHEAD PINNED

The cross head is firmly pinned to proximal tibia

PREPARATION FOR TIBIAL RESECTION

Raise the bar holding the resection guide and pin the bar to the upper tibia when the guide is centered on the proximal tibia.

The resection slot should be located a few millimeters below the lowest articular surface (usually medial).

Use the stylus to check the amount of tibial cut. 2 mm for medial referencing, 10 mm for lateral referencing.

FINAL TIBIAL CUT

The final tibial cut is completed with an osteotome to prevent over penetration of saw blade posteriorly which risked popliteal artery cut.

TRIAL TIBIAL BASE

10 mm base.

EXTENSION GAP

Extension gap is checked with Trial Tibial Base.

The extension gap should be able to accept a minimum of 10 mm base.

A symmetrical and rectangular extension gap must be obtained.

TRAPEZOIDAL EXTENSION GAP

The extension gap must be symmetrical, forming a rectangle.

Do not accept a trapezoidal gap as shown in picture.

If this is the case, release more soft tissue to get a rectangle.

The extension gap must be the same as flexion gap.

FEMORAL SIZING

Place the A-P femoral sizer flush against the resected distal femur and adjust the sizer so the feet contact the posterior condyles and the
stylus contacts the shaft of femur.

The anterior/posterior size is indicated on the distal face of the A-P femoral sizer.

If the sizing is between sizes, select the smaller of the two sizes.

ANTERIOR AND POSTERIOR RESECTIONS

Select the femoral resection block (4 in 1 resection block) corresponding to the size indicated by the A-P femoral sizer.

Place the femoral resection block flush
against the distal and anterior femoral surfaces.

Stabilize the block against the bone using 3.2mm diameter headed pins on the medial and lateral sides of the block.

The recommended order of resection is:

1. Posterior

2. Posterior chamfer

3. Anterior

4. Anterior chamfer.

SULCUS GUIDE FOR POWER BUR

2 styles of primary sulcus resection guide are
available: Standard Blade and Power Burr.

Shown here is Power Burr Guide.

Sulcus resection guide has the same size (Medio-Lateral) as the final implant.

TROCHLEAR GROOVE RESECTION

Trochlear groove resection with power burr.

TIBIAL SIZING

Assemble the trial tibial base equal in size to the femoral implant with the trial base handle and place against the proximal tibial surface.

If the size is appropriate, align the base and pin it to the tibia using short headed anchoring pins.

If the tibial size is too small, a "plus
size" will provide additional tibial coverage.

NOTE : The tibial insert size must match the femoral implant size.

There are two tibial base sizes that can be used with any one size femoral component.

For example a size 3 femoral implant can be
used with either a size 3 or 3+ tibial base

TIBIAL ALIGNMENT

An alignment rod can be inserted through the handle
to check alignment to the ankle

KEEL PREPARATION

Attach the keel punch guide to the keel punch handle and secure it to the trial base by turning the knurled handle.

Prepare the entry hole for the tibial stem using the 1/2" drill guide and oversize reamer .

KEEL PUNCH

Using the threaded punch handle and appropriate keel punch, slide the punch through the guide until the punch is fully seated.

The rim of the punch is designed to engage the trial base, keeping it from being inserted too deep.

The threaded handle has a mark indicating the depth that the punch should be impacted.

Once the punch is seated, remove the punch guide leaving the trial base and stem in place for a trial reduction.

TRIAL REDUCTION

With the knee flexed, place the appropriate size femoral trial on the distal femur using the femoral impactor.

Insert the trial tibial insert of equal size and appropriate thickness onto the trial base and complete the trial reduction.

PREPARATION FOR TIBIAL COMPONENT IMPLANTATION

Palacos bone cement applied on the cut tibial surface.

PREPARATION FOR FEMORAL IMPLANTATION

The femoral surface is coated with a layer of Palacos bone cement.

Palacos is chosen because of the longer setting time, thus allowing time for the surgeon to cement both femur and tibia components.

FEMORAL & TIBIAL COMPONENT IMPLANTED

After the metal base has been inserted, the appropriate trial tibial insert can be used to recheck ligament and soft tissue balancing

TIBIAL INSERT SEATING

Once the cement surrounding the tibial base has cured, the appropriate tibial insert may be locked into place.

Initial seating is accomplished by pushing the insert as far posterior as possible with hand pressure.

For final seating of the insert, an insert
assembly gun is utilized by placing the lower jaw in the anterior slot of the tibial base.

CLOSURE

Close the capsule and perform a "drop and dangle" test to predict the range of motion for the patient.

CLOSURE

Position the knee in full extension to continue closing the layers.

REHABILITATION PROTOCOL

The most important factor in gaining or maintaining high flexion after successful total knee arthroplasty is early and aggressive rehabilitation of the patient.

Many of the standard rehabilitation protocols are aimed at restoring knee motion and function between 90 degree and 110 degree, which is sufficient for the patient to get into or out of a chair or a car.

Patients who wish to maintain preoperative flexibility may be better off with early and more aggressive rehabilitation exercises.



Link List

Insall legacy

The Insall legacy in Total Knee Arthroplasty

Cemented and cementless Knee replacement

Cemented and cementless Knee replacement

Implant Design

Total knee replacement implant design

Post-op management

Post operative management

Postop Exercise Guide

Post-op exercise guide.

Minimally Invasive TKR

Minimally Invasive TKR